Rapid blood loss from relatively large surfaces is particularly difficult to control since it cannot be controlled by sutures or other ligation means. Attempts have been made to develop a haemostatic sponge which provides a fast and effective composition for inducing rapid blood coagulation and haemostasis at a wound or bleeding site. One such haemostatic sponge composition is an absorbable gelatin sponge. The spongy physical properties of the gelatin sponge hasten clot formation and provide structural support for the forming clot.
Gelatin sponges are made by whipping a solution of gelatin and drying the foam, usually by lyophilization. Unlike collagen which is naturally insoluble in aqueous neutral solutions, gelatin is soluble at temperatures above 30° C., especially at 37° C., the physiological temperature. This characteristic renders the sponge unsuitable for in vivo use as the sponge would dissolve quickly and loss its structural integrity and porous structure. The gelatin must therefore be cross-linked in order to prevent its rapid dissolution in the blood. Methods of cross linking include treatment of the sponge with a chemical cross-linking agent such as formaldehyde, glutaraldehyde, and carbadiimides (e.g. EDC) or via treatment of the dry sponge with dry heat (100-160° C. for several hours).
While its mode of action is not fully understood, it is currently believed that its effect appears to be linked to the ability of the gelatin sponge to absorb and hold within its interstices, many times its weight of blood and other fluids. Caught blood platelets interact with the sponge and get activated leading to the formation of a haemostatic plug and cessation of bleeding. This haemostatic plug resembles the natural plug that usually forms in the body after injury. The activated platelets also initiate the coagulation cascade that ends with conversion of soluble fibrinogen into a net of insoluble fibrin by the action of thrombin. Factor XIII which is activated by thrombin in the presence of Ca2+ cross-links and stabilizes the clot's fibrin monomers.
GELFOAM® and SURGIFOAM® are an example of haemostatic devices which can be applied dry or moistened with sterile saline or thrombin directly to the wounded site to obtain control of the bleeding. In order to enhance the natural haemostatic property of gelatin, products or kits that combine the haemostatic features of gelatin sponge, thrombin and Ca2+ have been developed and manufactured. For example, it is customary that in surgery the gelatin sponge is removed from its package, dipped into diluted thrombin solution and kneaded vigorously until all air is expelled. This step is followed by a second immersion in thrombin solution and application of the wet sponge to the bleeding organ with light pressure. However, the soaking of the sponge requires time-consuming and cumbersome procedures, including thawing and predilution of the concentrated thrombin solution. Each of the preparation steps introduces potential errors which might compromise the sterile preparation and vary the efficacy of the sponge. Moreover, the complicated procedure requires administration of the sponge by trained emergency personnel. Another major drawback in that technique is that a large volume of liquid is required to fill the sponge voids consequently resulting in a low concentration of thrombin and Ca2+ at the interface between the sponge and the injured site. As a result, the sponges are ineffective in providing and maintaining haemostasis. To overcome this problem, surgeons often resort to the use of high concentrations of thrombin, which may lead to local thrombotic events.
The following publications disclose coating of a cross-linked gelatin sponge with a solution of an active ingredient and drying the sponge.
U.S. Pat. No. 5,643,596 and WO9512371 disclose a haemostatic patch comprising a matrix such as absorbable gelatin sponge and an effective amount of epsilon aminocaproic acid (EACA) on only one side of the matrix. According to the description the matrix can be coated before and after addition of EACA with thrombin solution. The EACA can be applied by spraying powder, by coating a solution onto the matrix, or by complete or partial dipping. Drying of the wetted sponge is accomplished preferably by lyophilization. The patent application emphasizes the importance of EACA in the patch and is silent on a biodegradable matrix without EACA.
WO9013320 relates to a haemostatic sponge comprising a porous structure of biologically absorbable solid material such as denatured gelatin sponge, thrombin, and one or more thrombin-stabilizing agents. The hemostatic sponge is prepared by introducing into the sponge by injection at a multiplicity of sites an aqueous solution of thrombin. The injection is carried out without resulting in leakage of the injected liquid to the surfaces of the sponge material. The sponge is then air-dried at a temperature of 30-100° C. for a time a period sufficient to reduce the water content to below 50%. According to the description, the injection of the thrombin solution may result in structural deformation of the sponge.
U.S. Pat. No. 2,558,395 discloses a ready-to-use gelatin sponge containing thrombin. According to the patent, thrombin is added to an aqueous gelatin solution, transformed into foam and dried in vacuum at low temperature. The gelatin in this patent was not cross-linked at any stage during the preparation. Thus, upon contact with blood, the gelatin component is dissolved, the thrombin is released immediately and causes the transformation of fibrinogen to fibrin and a fibrin film is formed over the wound.
U.S. Pat. No. 4,292,972 relates to a lyophilized foam sponge product which has a hydrocolloid composition. According to the description the solubility and absorbability of the lyophilized foam product can be reduced by cross-linking either before or after the lyophilization procedure. The lyophilized foam product is formed from a mixture of gelatin, pectin and sodium carboxymethylcellulose.
U.S. Pat. No. 4,265,233 discloses a wound healing material to which factor XIII with or without thrombin have been fixed by covalent bonding, ionic bonding adsorption or entrapping. According to the description the wound healing material may be synthetic or natural polymers. The patent discloses several natural occurring proteins, including cellulose, viscose rayon, cupraammonium rayon, cellulose acetate, carboxymethyl cellulose, methyl cellulose, agarose, dextran, pullulan, pectin, alginic acid, chitin, polysaccharides such as mucopolysaccharides, and proteins such as wool, silk, collagen, gelatin and casein. The examples disclose dipping of a gelatin sponge in the size of 5×2.5×0.5 cm in 10 ml of an aqueous solution of factor XIII with or without thrombin and subsequent freeze-drying for 20 hours.
EP0277096 discloses hemostatic materials, such as GELFOAM®, SURGICEL®, and AVICEL®, and collagen which can be effectively used in combination with a stabilized thrombin formulation. According to the patent, the preparation must contain polyols and at least one buffer such as acetate or phosphate buffer. According to the description the stabilized solution is preferably absorbed onto the hemostatic agent and the pad is freeze-dried and packaged in a sterile manner.
WO02072128 discloses a cross-linked gelatin composition which has a wetting agent incorporated therein. According to the description the wetting agents can be coated over the surface of the gelatin sponge. The examples show that addition of the wetting agent onto the surface of the sponge is carried out by placing the sponge into a vial containing a solution of a wetting agent and a solvent. The vial is then inverted to allow the solution to soak into the sponge. The coated composition is then removed, drained of excess liquid and air dried overnight. According to the description the gelatin composition may also include a medicament such as thrombin, fibrinogen, factor XIII and other coagulation factors.
EP0568334 relates to a collagen-containing sponge comprising an absorbable gelatin sponge, collagen, and an active ingredient. The absorbable gelatin sponge can be combined with the collagen and the active ingredient by transferring a predetermined amount of a collagen solution on top of the gelatin sponge. The example discloses a preparation of a collagen sponge by pipetting 0.24 or 0.4 ml of collagen solution containing platelet-derived growth factor (PDGF) on top of a 1 mm gelatin sheet. Following soaking, the sponge is dried, preferably, at room temperature for a period of about an hour to about five days. It is indicated in the patent that in order to improve flexibility of the sponge a suitable plasticizer can be used.
WO9306855 relates to a haemostatic composition comprising a hemostatically effective amount of factor VIIa together with a biologically compatible carrier such as a biodegradable sponge material. The carrier does not contain thrombin or any other blood clotting factor. The description discloses several materials for the preparation of the hemostatic sponges such as collagen, gelatin such as denatured gelatin, chitin, cellulose, polyglycolic acid and polyacetic acid. The sponge may be prepared by saturating a preformed dried sponge with a solution of FVIIa followed by freeze-drying. The examples disclose soaking of 5 mm cores of gelatin sponge in 2 ml of sterile water which contained factor VIIa. The wet sponge was applied to the bleeding site without drying.